Mexico City's mayor, also seen as a leading presidential contender, has called for a mass campaign to keep adversaries from jailing him.

Mexico's Congress is to decide in coming months whether to strip Andres Manuel Lopez Obrador of immunity from prosecution enjoyed by public officials, and force him to face charges over a minor land-use case. Mr. Lopez could be jailed and barred from running for president if found guilty.

Speaking at a news conference Friday, Mr. Lopez Obrador said he would keep fighting and would campaign from a jail cell if he had to.

It was his first explicit statement of his plans to replace President Vicente Fox when Mr. Fox's final term finishes in 2006.

The central-leftist mayor of the Party of the Democratic Revolution is widely popular in Mexico City for setting up welfare programs for the poor and the elderly.